The spray painting of automobile bodies, engines and a variety of industrial and consumer articles is conducted in specialized enclosures called paint spray booths. These booths provide a controlled work area for the painting operations both enhancing worker safety and minimizing the possibility of contaminants adversely impacting the finished paint job. Booths can vary significantly in size and design but all have a work area where the actual painting is done and a backsection/underbooth area where paint overspray is removed from the air. In small or low production systems this is accomplished by pulling the paint laden air through a series of disposable filters. More commonly, a moving stream of air generated by booth exhaust fans pulls the paint overspray through a curtain or spray of recirculating water effectively scrubbing the paint particles from the air into the water phase. The water and scrubbed paint particles are carried to a sump basin where the paint particles are separated from the water so that the water can be recycled and the waste paint solids disposed of safely.
Paint is by definition a highly adhesive film forming material. It tends to readily adhere to any exposed booth surfaces where it can build and eventually reduce air and water flow, block drains, damage pumps and plug screens. This reduces booth efficiency and significantly increases operating costs. For this reason chemical “detackifiers” are usually added to the recirculating water. These act to improve the scrubbing efficiency of the booth, prevent the paint from adhering to booth surfaces and aid in the collection and removal of paint solids from the recirculating water stream.
In the past, solvent-based or solvent borne paints were most commonly employed in spray booths. More recently increased environmental awareness has resulted in Federal regulations limiting the amount of VOC's that can be released. This has resulted in an increased use of waterborne paints and reformulation of existing solvent based ones to reduce VOC's. These materials, while not as tacky as solvent based ones are much more difficult to separate from water and due to their surfactant load are much more prone towards generating significant amounts of foam and require different treatments than their solvent based analogs. Consequently a need has developed for “detackifiers” that cannot only reduce the stickiness of traditional paints but also deal with the need to control foam and improve collection of newer, reformulated water based and HAPS compatible solvent based paints (ones determined not to contain any materials regulated as Hazardous Air Pollutants). Current economic concerns and environmental awareness has also dictated that these products be cost effective and perform in a “green” sustainable manner.
A wide variety of chemicals have been proposed as treatments for wet spray booth waters containing oversprayed paint including water swellable clays, Mannich type polymers and amphoteric metal salts which form metal hydroxides at pH values >7. For example, U.S. Pat. No. 4,564,464—Teaches the use of pumpable, hectorite clay containing slurries, containing suitable thinning agents and water conditioning agents such as water-soluble phosphates. While able to treat both solvent and waterborne paints, this type of treatment generates excessive volumes of difficult to dewater sludge and tends to promote unwanted biological growth.
U.S. Pat. No. 4,888,386—Teaches the use of a melamine-formaldehyde based polymer in conjunction with a polyvinyl alcohol and a styrene acrylate copolymer to treat both water and solvent based paints very effectively. However, low levels of free formaldehyde present in this composition as with any Mannich type polymer have raised concerns for worker exposure. In addition, these materials are not easily biodegradable making sludge disposal a concern.
U.S. Pat. No. 5,068,279—Teaches a method for scavenging free formaldehyde from a high activity melamine-formaldehyde type detackifier to improve safety and reduce to VOC. This treated product performs well with all types of paints and is the current global standard. However, it is deemed “old” technology and concerns about formaldehyde and biodegradability persist.
U.S. Pat. No. 5,250,189—Teaches the use of polybasic aluminum salts such as preferably aluminum chlorohydrate (ACH) within designated pH and alkalinity ranges to provide improved collection of water based paints. Although this can do an excellent job in collecting water based paints the treatment provides poor detackification results with solvent borne paint due to the hydrophilicity of the aluminum salt.
A more recent innovation, U.S. Pat. No. 6,673,263B2—Teaches the incorporation of a minute amount (<0.5%) of a chitin-based polymer, “chitosan” under acid conditions to a dilute solution of aluminum chlorohydrate (ACH). The chitosan acts to partially crosslink with the aluminum salt as the pH is increased improving its efficacy as a coagulant. The addition of the chitosan is claimed to make the composition a “green” chemistry.
A Chinese Pat. No. 1919475—Teaches feeding a water-soluble cationic starch to the inlet of the recirculating water pump of a booth and an aluminum salt and/or polyamide based flocculant to the return line. This is potentially a significantly “greener” approach and initially appears similar to the present invention. However, the Chinese patent recognizes the inherent incompatibility of the three components and so requires feeding each component separately at a separate feedpoint using a separate pump. This imposes an extra level of difficulty on the process since the individual products must first interact with each other in relatively fixed proportions to effectively detackify and collect the paint solids. By feeding them separately the necessary balance becomes much more difficult to achieve on an ongoing basis.
Accordingly, what is needed is a single component, cost effective, “green” sustainable chemistry that can effectively detackify and collect all types of paint.